1. Field of the Invention
The present invention relates to objective optical systems used in applications such as investigating and imaging of cellular function, and more particularly relates to a small-diameter objective optical system suitable for in vivo examination of animals such as mammals.
This application is based on Japanese Patent Application No. 2007-216110, the content of which is incorporated herein by reference.
2. Description of Related Art
At present, a method for observing the behavior of molecules in biological cells and tissue labelled with a dye or fluorescent marker with a fluorescence microscope, a confocal laser-scanning microscope or the like is used.
The behavior of molecules in a living mammalian organism, such as a mouse, sometimes differs from that in culture, and therefore, observation of biological tissue and cells is carried out while the specimen is alive (in vivo). (For example, see Japanese Unexamined Patent Application, Publication No. 2006-119300.)
With conventional microscopes, such as laser-scanning confocal microscopes, it is not assumed that observation of various internal organs of small laboratory animals, such as rats and mice, will be performed in vivo. In examining the interior of a living organism, because the diameter of the objective lens in a conventional microscope is large, it is necessary to perform examination by first making a large incision in the organism. However, making a large incision is highly invasive to the organism, and therefore, it is not possible to carry out observation for a long period of time.
Furthermore, with the objective optical system in Japanese Unexamined Patent Application, Publication No. 2006-119300, although the tip diameter is small, the degree of invasiveness is still high when observing a site deep inside the brain etc. of a mouse. In other words, to observe the organs of a small laboratory animal, it is necessary to make an incision in the skin or muscle tissue, or to drill a hole in the skull to expose the internal organ. However, because the size of the objective lens to be disposed close to the observation site is large compared with the small laboratory animal or the observation target, when observing an internal organ etc. it is necessary to make a large incision in the skin or muscle tissue or to make a large hole. In such a case, although it is possible to carry out observation directly after making the incision or after drilling the hole, significant damage will be caused to the small laboratory animal. Therefore, it is difficult to carry out time-lapse observation over a long period of time. One approach that has been considered is to suture the specimen after observation and to make another incision at the next observation; however, if damage is caused to the small laboratory animal, it is difficult to perform observation under normal conditions over time, which poses a problem.